Facet joints and discs disposed between vertebral members permit motion between individual vertebral members. Each vertebra includes an anterior body and a posterior arch. The posterior arch includes two pedicles and two laminae that join together to form the spinous process. A transverse process is laterally positioned at the transition from the pedicles to the laminae. Both the spinous process and transverse processes provide for attachment of fibrous tissue, such as ligaments and muscle. Two inferior articular processes extend downward from the junction of the laminae and the transverse process. Further, two superior articular processes extend upward from the junction. The articular processes of adjacent vertebrae form the facet joints. The inferior articular process of one vertebra articulates with the superior articular process of the vertebra below. The facet joints are referred to as gliding joints because the articular surfaces glide over each other. As illustrated in FIG. 1, adjacent vertebrae V1, V2 have a disc D between their anterior bodies, and a facet joint FJ between articular processes. In the side elevation view of FIG. 1, only one of two bilateral facet joints FJ is shown. The spinal segment illustrated is a cervical spinal segment, but the present invention is not limited to treatment of the cervical spine. A foramen F, or opening, between adjacent vertebrae V1, V2 is typically occupied by nerves exiting from a spinal cord.
Vertebral manipulation and implants are often used in the surgical treatment of spinal disorders such as degenerative disc disease, disc herniation, curvature abnormalities, and trauma. FIG. 2 illustrates a spinal segment where inappropriate spacing between vertebrae V1, V2 has occurred as a result of some spinal disorder. The disc D and the facet joint FJ are shown in a compressed state and extending beyond their normal bounds. The foramen F is reduced in size by movement of the vertebrae V1, V2, and encroachment of disc and facet joint material. Reduction in the size of the foramen F may cause nerve compression and resultant pain and lack of nerve function. In some cases, spinal fusion is indicated to create appropriate spacing between vertebrae and to inhibit relative motion between vertebrae, thereby relieving nerve compression. Spinal fusion often involves the removal of the vertebral disc and insertion of an interbody implant to create a fused junction between a pair of vertebral bodies. Facet joints may be fused, including fusion with spacers, in conjunction with anterior vertebral bodies to complete the fusion between vertebrae. Facet joints may also be separately treated by fusion. Spinal fusion will be collective referred to herein to include one or both of anterior column vertebral body fusion and facet joint fusion. Facet fusion may be initiated by decorticating the opposing articulating surfaces and packing bone growth promoting substances or inserting implants into the spaces between the articular processes. Facet arthroplasty devices may also be implanted in facet joints after preparation of the facet joints. It may be difficult for a surgeon to determine the amount of contouring and shaping required for each of the articular processes. A trial-and-error routine may be performed as the surgeon removes a first amount of material from one or both surfaces and determines whether the spacing is adequate for receiving a fusion substance or device. An increased amount of precision is desirable for preparing the articulating surfaces to receive an implant or bone growth promoting substances. In some embodiments, such precision would minimize the possibility of producing excessive trauma and bone removal from the facets while optimizing the probability of improving or maintaining appropriate foraminal area and achieving a successful arthrodesis.
Spinal disc material is often detached and removed in association with spinal procedures such as discectomy, spinal fusion, and disc replacement. In these and other spinal procedures, facet joint or disc soft tissues have traditionally been detached and removed with grasping, clipping, cutting, and scraping instruments such as rongeurs, curettes, rasps, osteotomes, scrapers, burs, or sagittal saws. A shortcoming of many traditional instruments is a failure to provide limits to the movement and effective cutting zone of the instruments. Improved instruments and methods may increase patient safety and operational accuracy by incorporating limits to the movement and effective cutting zone of instruments.
Improved methods and instruments may also provide for one or more of instruments with leading edges configured to distract a space between bones into which they are inserted, and sizes and shapes that reflect the sizes and shapes of implants to be placed in a patient. Distraction instruments may be useful to properly space and align bones to be treated. Distraction instruments that also reflect the size and shape of implants to be placed in a patient provide for proper selection of implants without the need for an additional sizing instrument or template.